Air sampling: frequently asked questions and best practices
Q: What is viable microbial air monitoring?
A: Viable air monitoring is the practice of collecting samples of organisms suspended in the air (such as bacteria, yeast, and mold) onto growth media and then incubating the samples to see what organisms grow -- generally over 2-3 days for bacteria and 4-6 days for yeast and mold.
Q: Why is air sampling important?
A: Environmental contamination that makes its way into drugs can lead to health problems or even death in immuno-compromised patients. Mild contamination in food can lead to shorter shelf life, and severe contamination can lead to costly recalls. The specific threats vary by industry, but excessive amounts of bacteria, yeast, and mold in the air that can then make their way into your products is almost never “good.”
Q: How is viable microbial air monitoring different from using a particle counter?
A: A particle counter is a useful tool for quickly measuring how many particulates are suspended in the air. Particle counters cannot distinguish between viable and non-viable particulates, however, which is why comprehensive environmental monitoring protocols must also incorporate a viable air monitoring system such as the SAS Super 180 Air Sampler. Even if particles seem to be the size of bacteria, yeast, or mold: particle counters generally cannot tell if the organism is “bad” or benign. Per USP <1116>, “Monitoring of total particulate count in controlled environments, even with the use of electronic instrumentation on a continuous basis, does not provide information on the microbiological content of the environment.
Q: What is the difference between passive and active microbial air sampling?
A: Passive air sampling describes the use of “settle plates,” where an end user leaves out growth media such as a Petri dish, hoping microorganisms will fall onto the plate. Because certain microorganisms can stay suspended for an extended period of time – and the degree to which this happens can vary based on air flow, humidity, and size of the organisms/particles – this method can potentially miss serious contamination of small organisms. In contrast, active air monitoring such as that performed by all air samplers sold by Bioscience International, such as the SAS Super 100 and SAS Super 180, pulls air onto growth media at a set flow rate that is safe for the organisms (so they won’t die on impact prior to growth analysis) but fast enough to get a representative sample of all organisms in the air – even the particularly small and light ones. In addition to providing the end user with the ability to test for microorganisms down to 1 micron, this method also provides individuals with quantitative results that can be applied to action and alert levels. While an individual using settle plates can merely report the number of colony forming units (CFUs) found on their plate, active air monitoring allows that same end user to report their results in the format of CFU/m^3, which is essential for operational (and regulatory) purposes.
Q: What type of growth media do you recommend using when performing viable air monitoring?
A: The answer can vary by application, but malt extract agar (MEA) and sabouraud dextrose agar (SDA) are frequently used for testing yeast and mold growth, and tryptic soy agar (TSA) is a general purpose culture medium commonly used in testing for bacterial growth. Air samplers sold by Bioscience work with all forms of contact (55-65mm) and Petri (90-100mm) plates, enabling you to use the media of your choice without being locked into expensive, proprietary media.
Q: How often should I perform microbial air sampling?
A: The frequency of optimal air sampling varies by industry and application. For example, USP <797> Pharmaceutical Compounding – Sterile Preparations requires sampling at least every 6 months as discussed at https://biosci-intl.com/news/USP797_best_practices.htm but risk-averse organizations typically sample much more frequently. Food and biotech companies that want to minimize the risk of costly recalls or shutdowns in particular may choose to sample daily.
Q: If I find bacterial or yeast/mold in the air, should I be concerned?
A: Certain types of bacteria and yeast/mold are more problematic than others. It’s important to have a reputable company (or in-house organization) analyze growth and identify which specific organisms grow, if any. For example, food companies manufacturing fermented drinks and yogurts would generally not be concerned if they found beneficial gut bacteria in the air such as Lactobacillus Acidophilus. Other organisms, such as the fungus Aspergillus Niger (which can cause the disease commonly known as “black mold”), are generally never considered desirable.
Q: What levels of growth are “ok”?
A: The answer varies widely by industry and application. In the food industry, less than 100 colony forming units (CFUs) per cubic meter (1,000L) is generally considered ideal, and more than 300 CFU per cubic meter is considered to be a serious concern – as discussed at https://biosci-intl.com/news/viable_cell_counts.htm. In cleanroom and hospital environments, much lower levels generally would be required, such as those defined in USP <1116> Microbiological Evaluation of Cleanrooms and Other Controlled Environments.
Q: How should I incubate my samples, once collected from the air?
A:Incubation and analysis of air samples should only be done by experienced professionals. Generally, mold samples are incubated for 4-6 days around 26-30⁰C, while bacteria samples are typically incubated over 2-3 days in the 30-37⁰C range. For more discussion please see: https://biosci-intl.com/news/USP797_env_testing.html and https://jcm.asm.org/content/jcm/51/10/3172.full.pdf.
Q: Is it better to use a reusable or disposable sampling head on my microbial air sampler?
A: Both are generally good choices, depending on your operational preferences. Bioscience sells autoclavable AISI 316 stainless steel heads as well as pre-sterilized (irradiated), individually wrapped disposable heads that may be disinfected with 70% IPA and used for multiple samples during the course of a single shift.
Q: If I have an isolator unit, how can I sample the air for contamination without risking contamination during the test?
A: Bioscience sells the SAS Super Isolator model for this exact reason, where the control unit is stored outside the isolator, and only the stainless steel sampling head is installed inside the isolator.
Q: The FDA’s 21 CFR Part 11, and data integrity in general, are important to me. Are air samplers from Bioscience compliant?
A: Yes, air samplers from Bioscience can be used successfully in a 21 CFR Part 11 compliant environment. Our air samplers enable export to PDF as well as hardcopy printing, and various password controls are available on the units themselves to prevent accidental data deletion by operators. The units do not allow for any form of editing of historical data. Please consult https://www.fda.gov/regulatory-information/search-fda-guidance-documents/part-11-electronic-records-electronic-signatures-scope-and-application for more details as you implement 21 CFR Part 11 guidelines in your environment and plan your end to end workflow.
Q: How often should I have my air sampler calibrated?
A: The answer varies based on how much you use the units and what your risk tolerance is, but generally every 6-12 months, with six months being optimal for more risk-averse organizations such as pharmaceutical and medical device companies that conduct daily sampling. Compounding pharmacies and hospitals that sample less frequently may prefer a one-year calibration interval.
Q: Should I place an in-line filter in my microbial air sampler?
A: ISO 14698 does not mention the requirement of a filter. ISO 14698-1,2 in Annex A dictates that “exhaust air from the sampling apparatus should not contaminate the environment being sampled or be re-aspirated by the sampling device.” As long as you use a reputable, well-made air sampler that does not shed particles (such as from its motor or sampling head), a filter is not needed. Furthermore, most customers strongly prefer not to use a filter due to the inherent risk that the filter can trap and capture bacteria, effectively sharing and introducing contaminants across testing sites. A clogged filter can also impact the instrument’s calibration. The SAS Air Samplers sold by Bioscience have been validated in accordance with ISO 14698 guidelines and proven not to shed particles or introduce turbulence, as summarized at: https://biosci-intl.com/news/iso_14698.htm.
Q: How can I sample compressed gas to test for possible contamination?
A: Our SAS Pinocchio Super II compressed gas air sampler allows you to sample compressed air using the same impaction method as our SAS Super Air Samplers and meets all guidelines outlined by ISO 8573-7. For more details, please see: https://biosci-intl.com/products/sas_pinocchio.htm.
Q: Do you offer calibration and IQ/OQ services for your air samplers?
A: Yes! Bioscience employees are factory trained and certified to perform both air sampler calibrations and IQ/OQ validation services. Furthermore, Bioscience is accredited to ISO 17025:2017 for air sampler calibration by A2LA, and our accreditation certification can be viewed here.
Q: How long does an air sampler typically last, before needing replacement?
A: The answer varies by manufacturer, but Bioscience is proud that 99% of its air samplers sold since 1979 are still in use today! Batteries may need periodic replacement, but they are tested and replaced (when necessary—roughly every 5 years) at no additional charge as part of our regular calibration service.
Q: I have additional questions regarding how best to perform microbial air sampling in my environment. How can I answer them?
A: For additional questions, please contact us by phone or e-mail, and we would be happy to provide free consultatation regarding best practices for your air sampling needs.
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